Expandable, or swellable, packers are well known in the oil and gas industry and have been used for about a decade. These “swell” packers are typically used to block the flow of fluids through the annular space between the pipe and the wall of the adjacent wellbore or casing by sealing off the space between them. In operation, swell packers are controllably deployed to precise locations in the wellbore to provide basic functions, such as zonal isolation, casing protection, and flow control. Swell packers generally conform to the surface of the open hole and anchor the tool against differential pressure during operation. Such packers are especially well-suited for use in uncased holes or in old or pitted casing where slips would generally cause damage to or failure of the surrounding casing. Furthermore, swell packers can seal in larger holes or rough or irregularly shaped holes where compression type packers of the same nominal size would not otherwise seal. Due to their simplicity of actuation, swell packers are an attractive option for zonal isolation applications, employed in both cased-hole and open-hole applications.
Swell packers typically include a swellable elastomeric material, which expands upon contacting a selected wellbore fluid. The selected wellbore fluids may be water-based (including diluted acids and brines) or hydrocarbons or any other acceptable fluid. Generally, the greater the expansion of the swell packer, the faster the elastomeric material swells. Packers that swell prematurely, however, will engage the side of the wellbore before the wellbore completion is completely deployed into the well, thereby making impossible the safe delivery of the packer to the desired location. Such premature engagement can also cause the packer to shear, tear, or otherwise sustain damage, which may undermine the integrity of the sealing engagement between the completion device and the wellbore.
Since unforeseen delays may arise during wellbore completion operations, it is not always known exactly how long deployment of a swell packer will take. Thus, the swellable material can potentially be exposed to the wellbore fluid for an extended period of time, thereby causing premature swelling even in completion operations that include swell-delaying structures. Therefore, there remains a need for improved swellable packer elements that enable the effective use of swellable materials without premature activation.